cros: Initial structure for views-based lock.

ash/login/views/lock_screen.h

Index: ash/login/views/lock_screen.h
diff --git a/ash/login/views/lock_screen.h b/ash/login/views/lock_screen.h
new file mode 100644
index 0000000000000000000000000000000000000000..41a57058145ec0219697799e926fdd6706c30697
--- /dev/null
+++ b/ash/login/views/lock_screen.h
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+// Copyright 2017 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef ASH_LOGIN_VIEWS_LOCK_SCREEN_H_
+#define ASH_LOGIN_VIEWS_LOCK_SCREEN_H_
+
+#include "ash/ash_export.h"
+
+namespace views {
+class Widget;
+}
+
+namespace ash {
+
+// Fills the given widget with the lock screen view and displays it.
+//
+// The lock screen communicates with the backend C++ via a mojo API.
+ASH_EXPORT void ShowLockScreenInWidget(views::Widget* widget);
+
+}  // namespace ash
+
+#endif  // ASH_LOGIN_VIEWS_LOCK_SCREEN_H_